Autonomic Nervous System Drugs Practice Questions

Q: Which of the following is a short-acting non-depolarizing neuromuscular blocker?

Mivacurium. **Explanation:** Neuromuscular blockers (NMBs) are classified based on their mechanism of action (Depolarizing vs. Non-depolarizing) and their duration of action. **Why Mivacurium is correct:** **Mivacurium** is the only **short-acting** non-depolarizing NMB (duration: 15–20 minutes). Like Suxamethonium, it is metabolized by **plasma pseudocholinesterase**, which accounts for its rapid clearance. It is often used for short procedures where rapid recovery of muscle function is required. **Analysis of Incorrect Options:** * **Rocuronium (Option A):** This is an **intermediate-acting** non-depolarizing NMB (duration: 30–40 minutes). It is notable for having the fastest onset of action among non-depolarizing agents, making it an alternative for rapid sequence intubation. * **Suxamethonium (Option B):** While it is short-acting, it is a **depolarizing** NMB. The question specifically asks for a *non-depolarizing* agent. * **Pancuronium (Option C):** This is a **long-acting** non-depolarizing NMB (duration: >60 minutes). It is known for its vagolytic effect, which can cause tachycardia. **High-Yield NEET-PG Pearls:** 1. **Classification by Duration:** * **Short-acting:** Mivacurium. * **Intermediate-acting:** Vecuronium, Atracurium, Cisatracurium, Rocuronium. * **Long-acting:** Pancuronium, Doxacurium, Pipecuronium. 2. **Hoffman Elimination:** Atracurium and Cisatracurium undergo spontaneous degradation in the plasma (independent of renal/hepatic function), making them the drugs of choice in **liver or kidney failure**. 3. **Adverse Effect:** Mivacurium can cause **histamine release**, leading to hypotension and flushing if injected rapidly. 4. **Reversal:** Non-depolarizing blockers are reversed by Neostigmine (acetylcholinesterase inhibitor) or Sugammadex (specifically for Rocuronium/Vecuronium).

Q: Which of the following is the only non-catecholamine sympathomimetic drug?

Ephedrine. ### Explanation The classification of sympathomimetic drugs is based on their chemical structure, specifically the presence or absence of a **catechol nucleus** (a benzene ring with hydroxyl groups at the 3 and 4 positions). **1. Why Ephedrine is the Correct Answer:** **Ephedrine** is a **non-catecholamine**. It lacks the hydroxyl groups on the benzene ring. This structural difference has three major clinical implications: * **Oral Bioavailability:** It is not destroyed by COMT (Catechol-O-methyltransferase), making it effective when taken orally. * **CNS Penetration:** Being more lipid-soluble, it crosses the blood-brain barrier. * **Duration of Action:** It has a significantly longer half-life than catecholamines. Additionally, Ephedrine acts via a **mixed mechanism** (directly stimulating $\alpha$ and $\beta$ receptors and indirectly by displacing norepinephrine from storage vesicles). **2. Why the Other Options are Incorrect:** * **Adrenaline (Epinephrine):** A naturally occurring endogenous catecholamine. It is the drug of choice for anaphylactic shock. * **Dopamine:** An endogenous catecholamine and a precursor to norepinephrine. It acts on D1, $\beta$1, and $\alpha$ receptors in a dose-dependent manner. * **Isoprenaline:** A synthetic catecholamine that acts as a pure $\beta$-agonist ($\beta$1 and $\beta$2). **3. High-Yield NEET-PG Pearls:** * **Tachyphylaxis:** Ephedrine is notorious for causing tachyphylaxis (rapidly diminishing response) with repeated doses due to the depletion of norepinephrine stores. * **Clinical Use:** Ephedrine is frequently used to manage hypotension during spinal anesthesia. * **Mnemonic:** Catecholamines (**D**opamine, **E**pinephrine, **N**orepinephrine, **I**soprenaline, **D**obutamine) = **DENID**. If it’s not on this list, it’s likely a non-catecholamine (e.g., Amphetamine, Phenylephrine, Salbutamol).

Q: A child on Beta-2 agonists for the treatment of bronchial asthma may exhibit all of the following features EXCEPT:

Hypoglycemia. **Explanation:** Beta-2 agonists (e.g., Salbutamol, Terbutaline) act on $\beta_2$ receptors located throughout the body. The correct answer is **Hypoglycemia** because $\beta_2$ stimulation actually causes **Hyperglycemia**. **1. Why Hypoglycemia is the correct answer (The Exception):** Stimulation of $\beta_2$ receptors in the liver and skeletal muscle promotes **glycogenolysis** (breakdown of glycogen to glucose) and **gluconeogenesis**. Additionally, $\beta_2$ receptors on pancreatic islet cells increase insulin secretion, but the overall metabolic effect is an increase in blood glucose levels. Therefore, hypoglycemia is not a side effect; hyperglycemia is. **2. Analysis of Incorrect Options:** * **Tremors (Option A):** This is the **most common side effect**. It occurs due to the direct stimulation of $\beta_2$ receptors in the skeletal muscles. * **Hypokalemia (Option B):** $\beta_2$ agonists stimulate the $Na^+/K^+$ ATPase pump, causing an intracellular shift of potassium. This leads to decreased serum potassium levels. (Clinical Note: Salbutamol is sometimes used as an emergency treatment for hyperkalemia). * **Bronchodilation (Option D):** This is the primary therapeutic effect. $\beta_2$ receptors in the bronchial smooth muscle increase cAMP, leading to muscle relaxation and airway opening. **High-Yield Clinical Pearls for NEET-PG:** * **Muscle Tremors** are the dose-limiting side effect of oral $\beta_2$ agonists. * **Tachycardia** can occur due to direct $\beta_1$ stimulation (at high doses) or reflex tachycardia via $\beta_2$ mediated vasodilation. * **Tolerance (Tachyphylaxis):** Prolonged use leads to down-regulation of $\beta_2$ receptors. * **Drug of Choice:** Inhaled Short-Acting Beta Agonists (SABA) are the DOC for acute asthma exacerbations.

Q: Which of the following is NOT associated with beta-2 agonist treatment?

Hyperkalemia. **Explanation:**Beta-2 ($eta_2$) agonists act on G-protein coupled receptors to stimulate various physiological responses. The correct answer is **Hyperkalemia** because $eta_2$ agonists actually cause **hypokalemia**.**1. Why Hyperkalemia is the correct choice (The "NOT" factor):**$eta_2$ receptors stimulate the **Na+/K+ ATPase pump** in skeletal muscles. This causes an influx of potassium from the extracellular fluid into the cells. Consequently, serum potassium levels decrease (**Hypokalemia**). This effect is clinically utilized to treat emergency hyperkalemia (e.g., nebulized Salbutamol) [2].**2. Analysis of Incorrect Options:*** **B. Hyperglycemia:** $eta_2$ stimulation in the liver promotes **glycogenolysis** and **gluconeogenesis**. It also increases glucagon release from the pancreas, leading to elevated blood glucose levels [2].* **C. Detrusor relaxation:** While $eta_3$ receptors are the primary mediators of detrusor relaxation (e.g., Mirabegron), $eta_2$ receptors also contribute to the relaxation of the bladder wall (detrusor muscle), aiding in urine storage.* **D. Relaxation of gut and bronchial muscles:** $eta_2$ agonists cause smooth muscle relaxation via increased cAMP. This leads to **bronchodilation** (the primary use in asthma/COPD) and decreased gastrointestinal motility [1].**High-Yield Clinical Pearls for NEET-PG:** * **Tocolysis:** $eta_2$ agonists like **Ritodrine** and **Terbutaline** are used to relax the uterus and delay premature labor.* **Tremors:** The most common side effect of $eta_2$ agonists is muscle tremors, caused by direct action on $eta_2$ receptors in skeletal muscles.* **Tachycardia:** Even "selective" $eta_2$ agonists can cause tachycardia due to reflex sympathetic stimulation (vasodilation) and minor cross-reactivity with cardiac $eta_1$ receptors.

Q: Clinical signs of atropine intoxication are as follows, EXCEPT:

Increased bowel sounds. **Explanation:** Atropine is a competitive antagonist of muscarinic acetylcholine receptors. The clinical signs of atropine intoxication (anticholinergic toxicity) result from the blockade of the parasympathetic nervous system, leading to a "systemic drying" and "slowing" effect. **Why "Increased bowel sounds" is the correct answer:** The parasympathetic nervous system (via the Vagus nerve) normally increases gastrointestinal motility. Atropine blocks these M3 receptors in the gut, leading to **decreased intestinal motility** and constipation. Therefore, **decreased or absent bowel sounds** are expected; "Increased bowel sounds" is physiologically inconsistent with anticholinergic action. **Analysis of Incorrect Options:** * **Decreased bowel sounds:** This is a classic sign of atropine toxicity due to smooth muscle relaxation in the GI tract. * **Dry skin:** Atropine blocks M3 receptors on eccrine sweat glands (which are innervated by sympathetic cholinergic fibers). This leads to anhidrosis (suppression of sweating) and dry, hot skin. * **Scarlet flushing of face:** Known as "Atropine flush," this occurs due to compensatory cutaneous vasodilation in the blush area to dissipate heat, as the body cannot sweat. **NEET-PG High-Yield Pearls:** To remember atropine poisoning, use the classic mnemonic: * **Red as a beet:** Flushing due to vasodilation. * **Dry as a bone:** Dry skin and mouth (decreased secretions). * **Blind as a bat:** Mydriasis (dilated pupils) and cycloplegia (loss of accommodation). * **Mad as a hatter:** Delirium, hallucinations, and agitation. * **Hot as a hare:** Hyperpyrexia (especially in children). **Drug of Choice for Atropine Poisoning:** **Physostigmine** (a tertiary amine acetylcholinesterase inhibitor that crosses the blood-brain barrier).

Q: The action of adrenaline is potentiated in the presence of all the following anesthetics except:

Ether. **Explanation:** The core concept behind this question is **Myocardial Sensitization to Catecholamines**. Certain volatile anesthetics sensitize the myocardium to the arrhythmogenic effects of adrenaline (epinephrine), increasing the risk of ventricular arrhythmias. **1. Why Ether is the Correct Answer:** Ether is a **non-sensitizing** anesthetic. Unlike halogenated agents, ether does not sensitize the heart to adrenaline. In fact, ether causes a reflex increase in sympathetic activity, which actually supports blood pressure and heart rate without making the myocardium hyper-reactive to exogenous adrenaline. Therefore, the action of adrenaline is not potentiated (in terms of arrhythmia risk) by ether. **2. Analysis of Incorrect Options:** * **Halothane:** This is the "classic" sensitizer. It is highly potent in sensitizing the heart to catecholamines. Using adrenaline with halothane is strictly limited to avoid fatal ventricular fibrillation. * **Ethyl chloride:** This is an older, halogenated hydrocarbon that, like halothane, significantly sensitizes the myocardium to adrenaline. * **Cyclopropane:** Although not a halogenated gas, cyclopropane is notorious for its high potential to sensitize the heart to adrenaline, often leading to serious arrhythmias. **3. NEET-PG High-Yield Pearls:** * **Order of Sensitization:** Halothane > Cyclopropane > Trichloroethylene > Ethyl chloride. * **Modern Agents:** Isoflurane, Desflurane, and Sevoflurane have much lower sensitization potential compared to Halothane, making them safer for use when adrenaline is needed (e.g., for local hemostasis). * **Clinical Rule:** If adrenaline must be used with Halothane, the dose should not exceed **1 µg/kg**. * **Thiopentone:** It is also considered non-sensitizing to the myocardium.

Question 1

Which one of the following drugs does not produce central anticholinergic syndrome?

Accepted Answer

Glycopyrrolate

Answer

Atropine sulphate

Answer

Antihistaminics

Answer

Tricyclic antidepressants

Question 2

Which of the following is a short-acting non-depolarizing neuromuscular blocker?

Accepted Answer

Mivacurium

Answer

Rocuronium

Answer

Suxamethonium

Answer

Pancuronium

Question 3

Which of the following is the only non-catecholamine sympathomimetic drug?

Accepted Answer

Ephedrine

Answer

Adrenaline

Answer

Dopamine

Answer

Isoprenaline

Question 4

What are the effects of α-adrenoreceptor stimulation?

Accepted Answer

Vasoconstriction

Answer

Vasodilation

Answer

Bronchoconstriction

Answer

Bronchodilation

Question 5

A child on Beta-2 agonists for the treatment of bronchial asthma may exhibit all of the following features EXCEPT:

Accepted Answer

Hypoglycemia

Answer

Tremors

Answer

Hypokalemia

Answer

Bronchodilation

Question 6

Acetylcholinesterase inhibitors are not used in which of the following conditions?

Accepted Answer

Carbamate poisoning

Answer

Anticholinergic poisoning

Answer

Cobra bite

Answer

Glaucoma

Question 7

Which of the following is NOT associated with beta-2 agonist treatment?

Accepted Answer

Hyperkalemia

Answer

Hyperglycemia

Answer

Detrusor relaxation

Answer

Relaxation of gut and bronchial muscles

Question 8

Clinical signs of atropine intoxication are as follows, EXCEPT:

Accepted Answer

Increased bowel sounds

Answer

Decreased bowel sounds

Answer

Dry skin

Answer

Scarlet flushing of face

Question 9

The action of adrenaline is potentiated in the presence of all the following anesthetics except:

Accepted Answer

Ether

Answer

Halothane

Answer

Ethyl chloride

Answer

Cyclopropane

Question 10

Which of the following drugs has the maximum risk of causing dry mouth?

Accepted Answer

Oxybutynin

Answer

Trospium

Answer

Solifenacin

Answer

Flavoxate

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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